The present invention relates to improvement of a frictional transmission belt used for a belt-type transmission unit such as a belt-type accessory drive unit for an automobile engine. More particularly, the present invention relates to measures taken to eliminate an abnormal sound generated due to stick slip between the belt and a pulley coated with anticorrosion paint.
For example, a pulley used for a belt-type accessory drive unit for an engine is coated with anticorrosion paint at an automobile manufacturing site prior to shipment of a manufactured automobile to protect the pulley from rust during the shipment of the automobile to the user. Some of the coating is so rough that the paint comes off by idling the automobile for about 20 to 30 minutes, for example.
In some cases, however, even such roughly coated paint has not sufficiently come off when the automobile is handed over to the user. This causes generation of an abnormal sound due to stick slip between the coated surface of the pulley and the belt, and thus the user may file a complaint about this abnormal sound.
The abnormal sound is generated probably because the anticorrosion paint is tacky and this tackiness causes increase in the coefficient of friction between the pulley and the belt.
Conventionally, therefore, a material effective in reducing the coefficient of friction is attached to the surface of the belt.
The above conventional measure actually reduces the coefficient of friction and thus suppresses generation of an abnormal sound. However, with the reduction in coefficient of friction, there arises a new problem of deteriorating the belt transmission capability that is an essential matter for the transmission unit.
An object of the present invention is providing a frictional transmission belt looped over a pulley coated with anticorrosion paint, which suppresses generation of an abnormal sound, while maintaining the transmission capability as the frictional transmission belt, by suppressing only the tackiness of the anticorrosion paint.
To attain the above object, the present invention is based on the findings that the abnormal sound is generated mainly because the coefficient of static friction out of the two types of coefficient of friction, the coefficient of static friction and the coefficient of kinetic friction, increases by the existence of the anticorrosion paint. The present invention therefore uses a surfactant to suppress the tackiness of the anticorrosion paint. In this way, only the coefficient of static friction is reduced while the coefficient of kinetic friction is substantially maintained.
Specifically, the present invention is directed to a frictional transmission belt looped over a plurality of pulleys movably for torque transmission between the pulleys, wherein a surface-active layer made of a surfactant is formed on the surface of a belt body coming in contact with the pulleys.
When the frictional transmission belt looped over a plurality of pulleys runs between the pulleys, an abnormal sound will be generated due to stick slip between the frictional transmission belt and the pulleys if the surfaces of the pulleys coming in contact with the frictional transmission belt are coated with anticorrosion paint. The cause of this generation of an abnormal sound is considered to be as follows. The anticorrosion paint is softened and becomes tacky as the temperature rises with the running of the belt. This tackiness of the paint causes increase in the coefficient of static friction between the pulleys and the frictional transmission belt. As a result, stick slip occurs between the pulleys and the frictional transmission belt, and also the slip rate abruptly changes with a variation in the load of the frictional transmission belt on the pulleys. According to the present invention, the tackiness of the anticorrosion paint can be suppressed by the existence of the surface-active layer of the frictional transmission belt. This reduces the coefficient of static friction between the frictional transmission belt and the pulleys, and thus suppresses occurrence of stick slip between the frictional transmission belt and the pulleys. The surface-active layer hardly influences the coefficient of kinetic friction between the frictional transmission belt and the pulleys. Thus, generation of an abnormal sound is suppressed even when the anticorrosion paint has not yet come off, while the transmission capability of the frictional transmission belt is substantially maintained. This also provides a merit of smoothing the change of the slip rate with a variation in the load of the frictional transmission belt on the pulleys, as a spillover effect on the transmission characteristics.
The belt body may be a V-ribbed belt having a plurality of ribs each extending in a belt length direction arranged in order across a belt width on the surface of the belt facing the inside of the belt loop. Such a V-ribbed belt is normally used as the frictional transmission belt of a belt-type accessory drive unit for an automobile engine, and pulleys for the belt-type accessory drive unit are coated with anticorrosion paint prior to shipment from an automobile manufacturing site. In this occasion, therefore, the surface-active layer according to the present invention can practically act on the anticorrosion paint on the pulleys.
The surface-active layer may be formed by attaching a powdery surfactant to the belt body. With this construction, the surface-active layer, which is a powdery surfactant (for example, hand-washing powder soap) attached to the belt body, can be-easily formed on the surface of the belt body coming in contact with the pulleys.
The belt-type transmission unit using the frictional transmission belt described above may be a transmission unit including the frictional transmission belt and a plurality of pulleys over which the frictional transmission belt is looped movably, wherein a surface of at least one of the plurality of pulleys coming in contact with the frictional transmission belt is coated with anticorrosion paint. In this belt-type transmission unit, the frictional transmission belt looped over the plurality of the pulleys runs between the pulleys, and by this running, torque is transmitted between the pulleys. Conventionally, the belt-contact surface of the at least one pulley coated with anticorrosion paint tends to generate an abnormal sound due to stick slip caused by the anticorrosion paint. According to the present invention, however, since the frictional transmission belt has a surface-active layer on the surface of the belt body coming in contact with the pulleys, generation of such an abnormal sound is suppressed.